Topic 3: Organisms exchange substances with their environment

Question 1

what is the relationship between the size of an organism and its SA:V

Answer 1

the smaller an organism, the larger its surface area to volume ratio.

Question 2

outline gas exchange in single celled organisms

Answer 2

they are small and have a large SA:V so substances diffuse easily meaning no specialised system is needed

Question 3

describe gas exchange in insects

Answer 3

gas enters and leaves through spiracles that open and close via a valve
tracheoles are tubes that run along the length of the insect and supply it with gases

Question 4

describe gas exchange in fish

Answer 4

it is a countercurrent system. blood flows in one way and water flows in the opposing direction to maintain a constant gradient.

Question 5

describe gas exchange in dicotyledonous plants

Answer 5

mesophyll cells in the leaf

stomata on the underside of the leaf open and close to allow gas exchange

Question 6

adaptations of insects to reduce water loss

Answer 6

closing of spiracles using muscles

waxy cuticle and hairs to reduce evaporation

Question 7

adaptations of plants to reduce water loss

Answer 7

waxy cuticles
less stomata
hairs to trap moist air around stomata
stomata sunken in pits that trap moist air and reduce the conc gradient of water btw leaf and air

Question 8

outline the human has exchange system

Answer 8

air- trachea- bronchi- bronchioles- alveoli

Question 9

explain the process of inspiration

Answer 9

external intercostal muscles contract
internal intercostal muscles relax
diaphragm contracts and flattens 
volume increases
pressure decreases then air is forced in
this is an active process, it requires energy

Question 10

explain the process of expiration

Answer 10

external muscles relax
internal contract
diaphragm relaxes
volume decreases
pressure increases
air is forced out
passive process

Question 11

adaptations of the alveolar epithelium

Answer 11

large surface area

surrounded by a network of capillaries